Newborn mice of both sexes were injected from day 1 to 7 with 1 million international units of viral interferon provided by Dr. Gresser of Villejuif, Paris, France. Seven days after the last injection, 5 mg/kg of pre-formed antigen antibody complexes in 5 times antigen excess were injected intravenously. Serial blood samples were drawn as described in previous publications and the animals were sacrificed serially. Light, immunofluorescence and electron microscopic studies were performed.